1. Field of the Invention
This invention relates to valve constructions, and more particularly pertains to valve constructions in which a partial vacuum is generated in the course of fluid flow of a main stream for purposes of aspirating fluid in a connecting fluid passageway to a discharge point. In its broader aspects, this invention is directed to systems in which fluids such as hydraulic liquids are positively pumped from hydraulic cylinders or the like by means of hydraulic pumps effecting a true pumping action or by means of a partial vacuum effecting an aspirating action.
2. Description or the Prior Art
Control valves of the type hereinafter described in detail are used throughout the hydraulics and pneumatics industry for directing the flow of oil and air in hydraulic and pneumatic circuits. A common application of these valves is for use in controlling operation of lifting rams or pistons reciprocally movable in hydraulic cylinders. Such hydraulic cylinders which may be used for direct lifting purposes, reinforcing purposes, bracing, pushing and the like may be of one of two general types. These two types are single-acting and double-acting hydraulic cylinders. Single-acting cylinders employ a piston which is hydraulically extended and such extended piston relies upon the load, a spring member or gravity to effect retraction of the extended piston. In double-acting cylinders, however, the hydraulic fluid medium is employed not only for extending the piston but also in retracting the same in the opposite direction whereby the piston may attain its lowermost retracted position. Thus positive force is applied to the piston in opposite directions of movement.
Single-acting hydraulic or pneumatic cylinders encounter many practical difficulties, particularly in heavy duty applications. Heavy duty cylinder and piston systems are normally of a compact size whereby the piston weight is such that it will only force a minimum amount of hydraulic liquid from its housing cylinder. This fact combined with the frictional resistances afforded by the hoses and conduits employed in the supplying of hydraulic liquid to the cylinder and sealing devices used in the construction of the cylinder effectively prevent the weight of the piston from forcing the hydraulic liquid back to a reservoir.
The inability to retract present in typical single-acting cylinders leads to many practical operational difficulties. Thus when employing heavy duty cylinders in confined spaces, the piston in the extended position may create problems in endeavors to remove such cylinders to a new site of use. Obviously in heavy duty applications the extendible piston should be returned to a retracted position, as close as possible to a supporting floor surface so as to obtain maximum work benefits from such cylinder. Also when such cylinder is employed for reinforcing purposes or the like in a confined space, it may be necessary to pry the extended piston into a retracted position to enable such hydraulic cylinder to be removed from its original work position.
The use of pry bars in the prior art in connection with single-acting cylinders not only rendered use of such cylinders cumbersome, but in addition may lead to damage of the extendible piston.
In accordance with this invention an improved retractor valve is provided. In a preferred embodiment a single-acting cylinder is retracted without the need for a return spring or the use of hydraulic liquid application to opposed piston surfaces as is normally applied in double-acting cylinders. The valve embodiment provides retraction of the piston of single-acting cylinders when the cylinder is used in any horizontal or vertical position. In accordance with this invention, a two or three way directional control valve creates a partial vacuum within the valve interior which in turn creates an aspirating action. Such aspirating action performs a pumping function thereby the hydraulic liquid is exhausted in a ready manner from a work cylinder as in a jack construction or the like. In addition, improved retraction performance of spring returned single-acting cylinders is realized because the resistance to flow which slows the retraction of cylinders of this type particularly as the spring forces diminish near the retracted position of the piston are greatly reduced by the aspirating action of the valve.
The prior art has previously employed control valves for use with hydraulic cylinders for controlling the fluid flow into and from cylinders in which an extendible ram is disposed. Thus McClocklin, U.S. Pat. No. 4,049,019 is directed to a rotary valve providing desired fluid control when the extendible piston or ram of a hydraulic cylinder is in the extended or neutral position, is in the process of being extended or is in the process of being retracted. Other prior art control valves comprise Schultz, U.S. Pat. No. 3,677,295, McClocklin, U.S. Pat. No. 3,892,259 and Masuda, U.S. Pat. No. 3,556,151.
In all of the disclosures of these prior art references, however, there is no suggestion of the creation of a partial vacuum by means of fluid flow control so as to aspirate or positively pump hydraulic liquid from a hydraulic cylinder.
Ejector pumps of the type hereinafter described have also been employed in the prior art in a fluid handling environment as disclosed in Howard, U.S. Pat. No. 3,373,688, Stepp, U.S. Pat. No. 3,423,011, Haisma, U.S. Pat. No. 3,496,735, Shexnayder, U.S. Pat. No. 3,882,930, Yamoto, U.S. Pat. No. 4,549,854, Briley, U.S. Pat. No. 4,595,344 and Ise, et al, U.S. Pat. No. 4,600,363. In these references, however, there is no suggestion of the valve structures or systems of the invention hereinafter described in detail.